Meaning
Unintended gradual shifts in injection moulding parameters away from validated baseline settings cause part dimensions and physical properties to deviate over time. Automated quality systems monitor process window drift to detect ambient shop variations, hydraulic oil heating or heater band degradation. Parameter changes alter melt temperature, cavity fill rates and packing pressures across long production runs.
Detection marks the limit of stable processing and mandates parameter recalibration.
Thermal Instability
Variations in shop temperature between day and night alter barrel heat loss and mold cooling rates. Uncompensated thermal changes trigger process window drift, altering resin melt viscosity and part shrinkage rates. Closed loop temperature controllers correct thermal shifts before dimensions fail specification limits.
Viscosity Variation
Batch to batch lot changes in raw material melt flow rate alter cavity pressure profiles during injection. Experiencing process window drift due to resin viscosity shifts causes flash or sink marks on parts. Monitoring peak cavity pressure identifies material changes in real time.
Varying regrind ratios accelerates pressure shifts across shifts.
Control Boundary
Statistical process control limits define boundaries beyond which parameter drift yields non conforming parts. Automated sorting gates divert suspect components when process window drift exceeds set thresholds. Processors reset machine settings to restore central nominal conditions.
Unchecked process window drift causes dimensional non conformance.
